| Abstract: | Effect of extrusion conditions, particularly temperature, on the structure development of fibers from poly(ethylene terephthalate) modified with 60 mol% p-hydroxybenzoic acid was investigated. Light microscopy revealed that the structure of the liquid-crystalline fiber was highly dependent on the extrusion temperature: low-temperature-spun fibers exhibited a structure with domains or clusters of crystallites randomly oriented, whereas the fibers spun at high temperatures had a well-developed fibrillar texture. Anisotropy of the fibers, as evidenced by dichroism and by the variation of brightness or darkness of the fibers between crossed polars, was significantly higher for those spun at relatively high temperatures. Scanning electron microscopy revealed that the fibers spun at relatively low temperatures had poorly oriented, nonuniform morphology. Those produced at relatively high temperatures, on the other hand, consisted of well-developed fibrils. X-ray diffraction patterns showed that the molecular orientation increased with increasing extrusion temperature. A model for the development of fiber structure from thermotropic liquid-crystalline polymers is proposed. |
